text:
Why are there full-fledged entertainment systems on aircraft when today everyone has a smart phone?
Today, many large commercial aircraft have full-fledged entertainment systems, sometimes going as far as putting a personal LED screen in every seat.
Let's just consider the costs of this for a moment:
• weight of the devices and their wiring
• power and waste heat
• cost of designing and approving the system with the FAA
There may be more I missed.
So now let's consider that today, most people (and certainly most people who can afford to fly) have a smart phone of some kind. They will most definitely bring it with them on the flight. And most people will also bring the charger and headphones (or earbuds) with them.
So you can see where this is going. If the airliner wants to provide movies or music, why not just have a jack (USB?) at every seat to plug in your smart phone and get it that way? Or possibly even provide streaming Wifi once in the air (not a true connection to the internet at large, but just as a way to distribute the movies/music). There might still be bandwidth challenges, but surely, surely this is better than a traditional IFE system as it exists today.
Am I missing something?

Just for reference, Swissair Flight 111 crashed due to a fire associated with the IFE system.

@RonBeyer I didn't wanna mention it because of the large role the mylar insulation played in the fire. To me, the fact that IFESs are so heavy and add a wiring nightmare to the plane is enough to question them in light of ubiquitous smart phones.

@mins I'm not sure what you're saying. Note: not all IFESs offer their content for free. Advertising could just as easily be done via the streaming system to your phone, such as youtube does. Or if you really wanna get into business potential, we could consider an airliner partnering with netflix.

Have you considered the fact that an IFE system on a plane today was most likely ordered and installed several years ago?  Smartphones haven't been "ubiquitous" for that long.

Nate is very correct. Android is only 7 years old; iOS is 8. Many people still don't have, need, or want smartphones. I'm not one of those people, but they do exist.

Children or elders may not have their own phones, some passengers may come from a region where smartphones are not yet common. New or unsupported OSes may be used, apps must be maintained. Using private devices means providing support if the passenger has a problem connecting. Flight attendants will receive requests when phones are not configured properly. All this may create anger and dissatisfaction that can be relatively easily prevented.

I don't have a smartphone...Anyway I'd rather read a book on the plane.

Is there a reason for the downvote (EDIT: and closevote)? Up until then I thought I might earn some kinda easter egg badge for a question with 6 answers yet not votes.

For what it's worth, I fly Alaska whenever I can because they don't have this crap in my face the whole flight.  :-)  I'm often on my own laptop anyway.  The last thing I want is the endless nagging advertisements like I see on United.

Here are some points to consider:

The screen size is a huge part of the experience. People with smartphones mostly still view content on a large regular screen when they are home or at a hotel etc. Hence, given a choice a passenger is always going to prefer the larger screen you can pack into the seat back than the relatively smaller smartphone display.
If you can be sure every seat has an IFE screen you can use it for other purposes like mandatory safety announcements & videos. Unless  you can be sure there's no seat without a smartphone owner depending on them for such messages is hard
If you have an existing aircraft the cost & effort to modify it & recertify the changed config. isn't worth it
Smartphones have only become ubiquitous in the last 5 years.
Average fleet age is much more than that. A typical aircraft you fly on might have been built 10, 15 or even 20 years before today.
Manufacturing date is not as important as the design date: If you are flying even in a 5 year old aircraft but the design was made 20 years ago there's no chance the designer could even forsee the smartphone revolution so he put in the IFE.
New designs you can expect modifications e.g. Many recent aircraft have a local USB port you mention & allow the passenger to plug in his device & view his own movies or listen to his own music on the IFE screen. http://www.turkishairlines.com/en-int/travel-information/frequently-asked-questions/on-board/in-flight-entertainment

Connections enabling passengers to listen to, or watch on their
  individual screens, content on their personal iPods or USB devices are
  available on B777 and some of our A330 aircraft.

The power and waste heat tradeoff of smartphones vs dedicated IFE isn't clear: If you encourage IFE via smartphones you would need to provide charging capacity for simultaneous plug in of hundreds of phones. The electrical resources for that aren't  insignificant.
The devil you know is better than the one you don't: Dedicated IFE is tested & certified with well known characteristics. Having hundreds of unknown chargers plugged in & batteries charging adds other variables to the game. You'd also have to support multiple OSs, screen sizes etc. on the software side.

+1 for the fact smartphones have only been ubiquitous for around 5 years. Even though phones are now common, not everyone uses them for entertainment. Particularly the elder generation still only use phones for phone calls. Even if it were the case, it still takes time for airlines to refit cabins with newer entertainment systems, which is normally only done when it absolutely has to be done.

Also a point to consider, is that some airlines actually are starting to remove them now that many passengers have other means of entertainment: https://www.google.com/search?q=airline+removing+seat+back+entertainment&oq=airline+removing+seat+back+entertainment&aqs=chrome..69i57j69i64.6458j0j7&sourceid=chrome&ie=UTF-8

Some airlines (I've personally experienced Delta and United) use PDE (Personal Device Entertainment), where the passenger can download an app prior to their flight and entertainment/flight information can be streamed to their personal devices. You primarily see this on domestic flights, though some international flights do use this (i think more common on older airplanes).
Pros:

Less weight & cost per seat (no need for screens, power, mounting, remotes, etc.)
much cheaper 'upgrade' cost. Instead of upgrading every seat when things are outdated, you update the central server.

Cons:

Very hard to use the screen while eating, which in my personal experience is one of the peak times where everyone uses entertainment. Your personal device takes up tray table space, and no room for food tray.
placing your device on the tray table cranes you neck in a sometimes uncomfortable position. Bad for ergonomics. (especially when passenger in front is reclined.
Requires a download BEFORE the flight. In my experience, you're notified of this via email, which i'm sure many people don't read. I've heard countless stories of passengers finding out the hard way...they get on board only to find out you need to download the app, which requires an internet connection...which requires you to pay to access.
Supply for customers who don't have tablets/phones.
Now you need AC power to each seat to charge said personal devices. What if you're on a 18hr flight. I'm 99% sure most devices cannot last that long streaming video.

Based on the market and the flight, you can see that the carriers choose built-in screens or BYOD. Shorter flights may make more sense to have them bring their own device. On long int'l flights, you're aiming for in-seat IFEs to make the journey more comfortable.

for your personal experience, and you are right that most devices will not last 18 hours streaming video. However, to fix that, a simple USB jack or even traditional power outlet per seat will be enough. I am 99% certain that this will cost less electric power than a larger screen per seat. Also, based on the market and the flight, I cannot see that the carriers choose built-in screens or BYOD. We haven't even calculated how much fuel is lost to the weight of of the IFE, which will be greater on longer flights.

Also, I wanted to say that the carriers are being very stupid to require to download their app before boarding. It is not that hard to setup local wifi on the plane with a local server that can distribute the app, and will weigh much much less than a traditional IFE!

@DrZ214: It feels like you're not really thinking this through. For example, iOS cannot install an arbitrary app from an arbitrary server like Android can with side-loading.

@GregHewgill Of course not, but for a large airline, getting a free app signed on the app store is a piece of cake. Now arbitrary server, like wifi on a plane already in the air, i'm not so sure about. Worst case, just use web pages with embedded content---streaming media, interactive java apps that show flight data, etc.

@DrZ214 "I am 99% certain that this will cost less electric power than a larger screen per seat." I'm not so certain. You'd be surprised how much power some smartphones, let alone tablets, can pull down. And that's to say nothing of the pax who use a laptop with a 150W charger. The IFE is probably in the neighborhood of 0.5 to 1 W for the SOM and a few W for the screen (at most.) Remember that phones are not only powering their screen when plugged in, they're also charging their batteries. Granted, that's actually a very useful feature and many airlines offer it intentionally.

For what it's worth Southwest also offers the ability to stream TV shows and movies to your device similar to Delta on their Wi-Fi equipped aircraft. Personally, I've had better luck with Southwest's system actually working than with Delta's.

@reirab I know from personal programming experience that the screen is one of the biggest power-drawers for smart phones. Note however that it depends on the brightness. I personally turn my brightness all the way down almost all the time, which I'm sure most people do not do. Also, a bigger phone/tablet will have a bigger battery, so you might not notice it, but I can assure you they draw much more power. As for laptops, those draw a lot more power because they have cooling fans plus a much much much "bigger" processor, to say nothing of spinning CDs or harddrives. Also, what is "SOM"?

@DrZ214 SOM = System-On-Module Could also be a System-on-Chip (SoC), but the difference is mostly academic for the purposes of this topic. You're right that the screen uses most of the power when running on battery, but you're not considering that, when you plug the phone in, it's charging the battery. So, when pax plug in their phones, you're powering the phone and charging it. Phone (and especially tablet/laptop) chargers can pull a significant amount of power.

@DrZ214 It's worth noting, though, that phone/tablet processors use a lot more power when doing graphics-intensive stuff. While normal apps will have the CPU nearly idle (and in a very lower power state,) playing movies and (especially) games will draw a lot more power from the CPU/GPU. The processor in my Surface has a thermal design power around 15 W, IIRC. While it normally pulls nowhere near that, open up a 3D game at high resolution and suddenly it will.

@reirab yes it's true charging battery + using phone draws more power. I finally found some #s. Looks like the typical phone battery holds 44.28 kJ. So let's say you charge it from 0 as u use it for, say, a 4-hour flight. Let's just say that requires 5 "charges" of energy total, or 221.4 kJ. And lets say 300 passengers. So 66.42 MJ. IIRC, gasoline chemical energy holds around 42 MJ/kg. I believe jet fuel will have more octane, but if we just accept 42 MJ/kg, and even factoring in a 10% (in)efficiency of the jet engines' power gen, we only need 15.8 kilograms of fuel to cover this.

@reirab But I hafta admit I am still kinda shooting myself in the foot because a modern IFE will use about the same energy...even less since it's not charging a battery. That applies to modern IFEs, not old ones. As several commentators have pointed out, there are surely still many old IFEs flying around. My gripe with power might've been ill-founded, but I will still say that the wiring nightmare of an IFE has not gone away. It's not just a weight and plumbing nightmare. Any complex network of wires is a major safety concern for arcing and making sure they remain cool and unchaffed.

@DrZ214 Yeah, I suspected the fuel consumption would be a rounding error, since the systems would use a total of maybe 2 kW, whereas the jet engines can produce 150 MW or more of total power output on a large airliner. Also, arcing usually isn't a concern with 12 V lines, let alone the fraction-of-a-volt data lines.

@DrZ214 Technicalities aside, i personally prefer a built-in system. I can eat and watch a movie at the same time. I don't have to fumble around for my tablet charger (which i swear many in-seat AC ports never work), or worry i'll fall asleep with the tray table still out and tablet running. I can play games on my phone while watching. Neck strain. Just to name a few.  If i'm paying thousands for an int'l flight with food service, I'd expect built-in IFE.

Today's IFE systems aren't solely about entertainment media. They might also show flight status, let your order meals, offer flight-specific destination information, etc. Now none of this is impossible to do with, say, a local WiFi network and a local web server. However:

The typical IFE screen is larger than a smartphone, which is easier for viewing movies
You don't have to hold the screen if it's mounted in the seat in front
Flight crew would need to be trained in at least basic troubleshooting of passenger devices
An alternative would still need to be provided for passengers who did not have a suitable device

I cant agree with everything you said. Yes, IFE screen is larger, and yes, you would have to hold your phone. Is this really that big a deal? Most users are used to watching youtube on their phone. The #1 selling point for flights is not what entertainment they offer, but ticket cost. We have not even gotten into extra fuel costs of the IFE, but IIRC most weigh 3000 lb or more. Finally consider that many IFE content are not even complimentary. The passenger has to pay if he wants it. So most don't, and so the idea of this 3,000 lb IFE flying around on every flight gets real dumb real fast.

@DrZ214 " IIRC most weigh 3000 lb or more" That sounds extremely unlikely to me (as one who designs embedded systems not dissimilar to IFEs professionally,) at least for narrow-body aircraft. That doesn't even sound probable on a 400 passenger aircraft (unless it's one of the ones that had HDTVs and such in luxury First.) For a 150 pax aircraft, that would be 20 lb/pax. I'd guess most of the systems I've seen don't weigh more than 2 lb/pax.

@DrZ214: It might be different around where you live, but the people that are around me are only watching full videos on their smartphones if there is no other choice and they are bored by other stuff. The occasional cat video, yes, but not full movies. They prefer larger screens that they don't have to squeeze their eyes to see anything (yes, a lot of those people that I know don't have perfect eyes). Also I never looked/asked for that but I doubt that many people will want to hold their phone for many many hours.

@reirab I might be recalling dated information, possibly even having to do with an IFE that used CRTs every 6 rows or something like that. But who knows, maybe 10 years ago flat screens were 4x as heavy as today? These days (2016) flat screens can be much lighter. But as a few commenters have pointed it, we still have IFEs from planes 5, 10, even 15 or 20 years ago flying around today.

The real answer is in @curious_cat 's answer but it needs to be emphasized:
it's the safety videos.
Per FAA Advisory Circular 121-24C:

The pretakeoff oral briefing may be given by
  audiotape or videotape means. This method of passenger briefing should be considered when
  the aircraft is equipped with the necessary videotape and sound equipment. The advantage of
  audiotape or videotape presentations is the assurance that a complete briefing is given, that the
  diction is good, and that an overall high quality briefing is maintained. Tape presentations also
  lend themselves very well to a multilingual presentation. In addition, a videotape presentation
  can include “signing” for the deaf and other visual presentations, which may be more meaningful
  to passengers.

There you have it. Showing a videotaped safety demo ensures the FAA won't fine you to oblivion because some passenger filed a complaint that the demo was not satisfactory. Believe me, airlines do not want to cross the FAA.
Advertisment and movies are gravy. It just means some of the costs you can chalk up to marketing. Good for you.

The FAA is being a bit near-sighted here, but a careful reading shows they allow this: recorded audio presentations can serve this purpose and retain most benefits, including good diction. All large commercial planes have speakers so audio can reach everyone. Just a real-life example here: my local library has not figured this out either. Every evening, some poor sap dictates word-4-word the same closing announcements as the night before. Well almost word-4-word. Recording and playing back the audio would eliminate the stutters, slips, & hesitations. Talk about bureaucracy vs business!

@DrZ214 Recording the closing announcements at your local library would require staff time, knowledge of audio recording, recording equipment, playback equipment, and staff to trigger the recordings. It's not clear to me that this is really easier than just making a nightly PA announcement.

@ZachLipton You seem to be thinking of a very analogue solution such as a sound studio. These days, all you need is a computer and a program like audacity. It would not take any more time to hit the record button while the announcer makes his announcement, which he was gonna do that night anyway. It does not take much time to save the file then set up a program to automatically play it back at fixed times each day either.

From my perspective using a smartphone/tablet has a few issues.

Usually when traveling I like to be able to communicate, which means my smartphone is off-limits when it comes to playing games/watching movies so I can save my battery in case I have issues at one of my connections or my destination. (Power outlets at airports are like gold, although they are becoming more common). Its a possibility to provide charging for devices in the aircraft but look at the issues associated with that, perhaps somebody plugs in a high load device, or an overheating charger, etc. If the system is approved, it should be safe, BYOD is giving up that approval process and trusting your fellow passengers that their equipment is in good working order. How many people have had iPhones blow up in their pockets or on chargers?
Even if I could use my smartphone, the issue becomes proping it up on the tray and getting a major neck-ache from looking down at it, along with eye-strain from watching a 5.7" screen (which is huge by todays standards).
For a tablet, it requires me to also prop it up somehow and stare at it, while the screen is typically larger than the IFE system, its still not ergonomic. I much prefer watching something on the back of the seat where I don't have to look down.
All that being said, I still have to download the movies I want to watch and store them on my device, which I really have better things to do with the space they take up. Its nice being able to choose from a list of channels (like Uniteds DirectTV service) or a good list of movies.
Some airlines (I know United does this) have movies available to watch that are not out for purchase or home use yet. Sometimes I get to catch movies in that space where they aren't in the theater anymore but still not out for purchase.

So personally coming from somebody who flies commercially quite a bit, I prefer the IFE over my smartphone/tablet. Its nice being able to lean my head back and watch the video. If the airline ever lets us mount our smart device on the back of the seat ahead of us I may change my opinion, but right now I don't think they would take too kindly to that.

a few questions/points: 1. How many people have had iPhones blow up in their pockets or on chargers? Are you being facetious? I know no one who's had that happen. If you're serious, slow charging is safer (e.g., connecting phone's usb to computer). 2. Doesn't every modern smart phone have a kickstand (optional accessory u can buy) to prop it up at any angle? 3. The problem of downloading a huge movie is side-stepped with streaming. Streaming only buffers/caches one portion at a time, which is continually overwritten by the next portion. 4. United could still do that under a streaming system.

no, it doesn't

No, I'm not being facetious, and its a battery issue not a charging one, although it seems to be mostly resolved as of late. 2. No, but regardless of the angle, it still has to be placed on the tray requiring you to look down at it. 3/4. Streaming has some DMCA/DRM issues that may not allow the carrier to stream them, especially with pre-releases.

Also, regarding #1 of your question, some phones/tablets won't "slow-charge", my Nexus 6P won't charge without its 3A charger (which is USB-C, not A/B), and my Samsung Tab Pro 8.4 won't charge with less than 2.5A (outside of the USB A/B spec).

Also, getting the content onto your device in the first place can be hard, especially when travelling abroad.  For 2x5 hours flights, + 2x3 hour train journeys that's 16 hours worth of content you'd want to pre-download onto your device - and due to geo-blocking you'd need to do this before leaving your home country - assuming your preferred service offers downloading (e.g. nothing from My5, YouTube or Netflix).  And even when flying on an airline like Thomas Cook with at seat USB charging points - after a long delay you might end up on an older aircraft with no charging point & a flat battery

Consider an entirely different perspective - airlines are forever trying to differentiate their products and the in-flight entertainment is one area that airlines tend to compete or display their edge.
Many airlines specifically advertise the features of their entertainment systems as part of the perks of flying the airline - as technology becomes more ubiquitous and embedded, I can only see more innovation in this area - rather than the reverse of removing the option completely.
Practically speaking; there are some other concerns with the BYOD concept:

You cannot get airline-customized information on your personal device - for example, the outside camera views on Emirate aircraft or the cockpit radio transmissions that you can tune into on some United flights. I am sure it would be possible to do this, but the hassle of supporting a large sea of various devices is not worth it in the long term.
As mentioned by others, there is a safety concern here. Any equipment has to be certified and it may be difficult to get all cellphone manufacturers to agree to a standard to be compatible with all the various aircraft and seat configurations. In addition they are required to provide a uniform experience when safety videos are shown.
Personal technology moves at a faster pace and is subject to different controls and regulations than aircraft and airlines. It would be very expensive for airlines to make sure the seats on their aircraft are compatible with all the various types, configurations, screen sizes, power requirements for personal entertainment devices.  Aircraft also have a longer service life than personal electronic devices.

Although airlines are starting to integrate personal devices into their infotainment systems - those screens are there to stay for the long term and will only get more integral to the flight experience.

Because not everyone has a smartphone (I don't, for instance).  Smartphones are pretty damn expensive compared to dumbphones, with both the initial cost of buying the phone and the ongoing cost of a talk+data plan being higher than the dumbphone equivalents.

authors: Vladimir F Героям слава


text:
What is a Polar airplane?
I stumbled on a new chinese one here: The "Snow Eagle 601".

Can someone expand a little?
At first sight, I can't make any relevant difference from a regular one (It just looks like a stock DC3 fitted with new turboprop engines + snow skis for the purpose).
Anything to do with the plane's performance required by the toughness of elements in the poles?

The aircraft is a Basler BT-67, which is a retractable wheeled ski equipped undercarriage STOL aircraft. It is a remanufactured DC-3 with Pratt & Whitney Canada PT6A-67R turboprop engine. The modifications include lengthened fuselage, increased MTOW, new avionics, redesigned wingtips etc. The skis are added in Canada.
Reports indicate that the aircraft includes an ice radar system, airborne gravimeter, airborne magnetometer and onboard laser radar system.
It is called a 'polar' airplane because it is owned by the Chinese Arctic and Antarctic_Administration. The aircraft is used by quite a few other missions in Antarctica, like Australia and the US, all operated by the Kenn Borek Air.

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How to interpret ATIS ground communication
Let's say I have the following ground communication from ATIS:
> Gillespie tower information Charlie,
> Time 1547 zulu, wind 250 at 20
> Visibility 7, Ceiling 1000 overcast
> Temperature 18 / Dewpoint 14
> Altimeter 30.90
> Localizer Delta approach in use, landing and departing runway 27R and 27L.
> Advice on initial contact, you have information Charlie

I more or less important the important bits but I don't understand the nuances.
What I understand:

"Charlie" means I have to listen to the weather report for time-period Charlie (since there are alpha, bravo, charlie, delta weather reports, corresponding to 4 time periods during the day).
1747 means 5:47 pm.
Wind at 270 degrees at 10 mph
Temperature 18 is 18 degrees Celsius
Set altimeter to 30.01 as that is the pressure altitude on the field
"Advice on initial contact, you have information charlie" means when I talk to ground for requesting taxi to runway or something, I notify ground that I have "information charlie"

Questions:

What is the relation between zulu time and PDT time. Given zulu is universal, how do I convert between local time zones?
With the visibility numbers, is higher better or worse?
With dewpoint numbers, is higher better or worse?
What is localizer delta approach in use? Is "localizer delta" the name of some kind of jet?
What does it mean when it says "landing and departing runway 27R and 27L?

Some of these questions might be really obvious to most, but I am a new student pilot in training for my PPL, so it's still a bit new to me.

This may be useful for many of your questions: https://aviation.stackexchange.com/questions/25231/why-do-pilots-need-the-ceiling-time-and-dew-point-in-the-atis

@BillLynch I must have missed that question. I'll update my post

Understanding:

The ATIS letter codes state which ‘version’ of the ATIS you are listening to, which can be communicated in a simple way to ensure you are up to date. The letter / version advances when either a significant change occurs in the weather or routinely as per the airfield regulations (such as every hour). ATC can ask if you’ve copied information C and you respond yes or no, simple.

Yes. 24h clock.

Nautical miles per hour. Not statute (regular) miles per hour.

Yes

That is the altimeter setting for correct density altitude at your field. Pressure altitude would be from an altimeter setting of 29.92.

Correct, as per 1.

Questions:

UTC is PDT + 7. Google it.

Visibility is measured in statute (“regular”) miles    in North America and metres everywhere else. Bigger is better and you will learn what the minimum required visibility is for visual flight.

Dew point is a temperature measured in degrees Celsius. We can use this to predict a rough altitude where cloud will start to form and also for performance considerations as linked by other members. The number itself is important (in more than just a “bigger or smaller is better” way) but the gap between it and the OAT is also important. You should learn about this on your road to your PPL

This message is stating the primary instrument approach that is in use. A localiser is a type of instrument approach and delta is the variant of it. These can be found in the terminal approach plates for the airfield. You’ll learn about these when you start your instrument rating training.

Some airports have preferential runways for departure and arrival to help traffic flow or to avoid certain parts of the airspace for noise or terrain reasons. So to aid forward planning, the ATIS will tell you which runways to expect for departure and arrival. In this case both 27L and 27R are being used for both departures and arrivals.

Of interest, the -D suffix in the name of the LOC-D approach at SEE indicates that it is a circling-only approach (no straight-in minima are published). Given that the suffix is -D one would expect there to be at least three other such circling-only approaches to SEE (A, B, and C), but in fact the LOC-D is the only one. Strange.

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text:
Climb calculation from meteorology ground school
I have problem understanding what kind of answer is expected in meteorology question as follows:
How many feet must you climb through to reach FL 85?

Given: FL 85
Departure field elevation 1500 ft
QNH 1013 hPa
Temperature ISA -10deg C
1 hPa = 27ft

Is it asking about an indicated altitude change or about a true elevation difference?

If this was about indicated, altimeter set to 1013 hPa at 1500ft aerodrome at ISA-10deg C would show as 1560ft (am I applying compensation of 1% per 2.5deg C correctly?). Therefore to change its indication to 8500ft, aircraft must make a climb of indicated 6940ft? That makes answer makes sense for me, since it would represent something that is visible on AI and VSI.

On the other hand, if the question is about true elevation difference, FL85 would be indicated around 8160ft elevation at ISA -10deg C (again, is this correction in the right direction)? To climb from elevation 1500ft, it would require 6660ft elevation change. That answer feels pretty useless, since no instrument would show that (apart from a GPS or some radar).

The answer accompanying the question suggest to calculate difference of 7000ft and compensate 1% per 2.5deg C that to get 6720ft. That does not feel to correct to me at all, since it completely ignores initial elevation/altitude.

If I am using incorrect terminology anywhere, I would be happy to correct that.

The post has both "FL75" and "FL85" - which is correct? Also, please understand that a vague question is vague for everyone, as nobody here has mind-reading insight into what an author intended about his question.

I agree with the previous comment. The test question appears to be designed to test your comprehension of the difference between true altitude of 1500' at the field, and flight level altitude at some height (7500' or 8500'...your own post is unclear on that point), as flight level altitudes are not the same as true altitudes. But a) your own post is presented in a hard-to-understand way, and b) asking a group of strangers what some third party meant when they wrote something is only going to get opinion-based answers. No one here can definitely state what the test question means.

In the queue to be closed because it would be “opinion based”?  I”m voting to keep this question open on a site that is supposed to be where experts answer questions, from the general public.

@RalphJ thank you, corrected to FL85

@PeterDuniho
b) I believe it is still worth asking this here, maybe this is better explained in other ground schools materials - I was only provided explanation 3).

Answer (3) would make sense in that 7,000' is the distance that you're climbing.  Those 7000 feet are "indicated" feet, and maybe the temperature correction coverts those to "actual" feet climbed... somebody closer to ground school would have to tell you if that's correct or not.  It's been a long time since I cared about any feet besides those read on some sort of altimeter, or the ones inside my shoes.  But really, asking your ground school instructor about this might be the most productive approach to understanding the material that the question is testing you on.

Turns out the answer 3 is indeed correct, but a shortcut is being taken in the solution that muddies things up.
First, consider the more sensible question about climbing to $8,500\ \mathrm{ft}$ indicated at the airfield altimeter setting. Clearly you need to apply the $10°\mathrm C\times\frac{1\%}{2.5°\mathrm C}$ correction to the $7,000\ \mathrm{ft}$ of difference. That's how the correction works.
Now you have FL85 instead of $8,500\ \mathrm{ft}$. Alas, the altimeter setting is $1013\ \mathrm{hPa}$, which means the FL85 does, after all, coincide with $8,500\ \mathrm{ft}$ indicated.
The step to flight level seems to be there just to confuse the otherwise easy question, while also making it less realistic. If the airport was surrounded by $8,000\ \mathrm{ft}$ peaks, you would want to know whether flying $8,500\ \mathrm{ft}$ indicated still gives you enough terrain clearance, but you never fly flight levels unless you are sufficiently far from the terrain that you don't need to care.

Flight levels appear to be based on a standard sea level pressure of 1013.25 hPa or 29.92 inches mercury.
Above a Transition Altitude one switches from local "QNH" to standard pressure.
Standard temperature is 15 °C at sea level, decreasing 2 °C every 1000 feet.
Since (cooincidentally) your QNH is 1013 hPa, you would climb to 8500 feet Indicated.  (You would not have to reset your pressure gauge).  Easy.  Everyone else above the TA is at the same pressure setting.
To calculate your actual distance climbed figure the standard temperature at FL 8500 should be -2 °C and ISA -10 °C.  This means that your Outside Air Temperature or OAT will be -12 °C at 8500 feet. (This can be verified!).
The rule is 1% correction every 2.5 °C, so a 4% correction, or 8500 feet × .04 = 340 feet.
That works out to actually climbing 8500 - 1500 - 340 = 6660 feet
to FL 85.
Note that the ISA deviation is given for 8500 feet.  When your altimeter, set to 1013 hPa, reads 8500 feet, because of the temperature difference, your actual altitude is 8160 feet.
Therefor, the temperature correction must be applied to the entire 8500 feet, not just 7000 feet above the airfield.

The temperature is specified as ISA-10°C, not as -10°C@FL85, so you should be getting 4% correction.

@JanHudec  Difficult to answer without clarity, but we try!  QNH 1013 must read out as 1500 feet, or it might be a bad day at that field.  Standard temperature at 8500 feet is - 2 C.  Need clarification where - 10C is at,  but as John K pointed out, colder than standard will show higher altimeter than one really is.  So the climb to 8500 indicated will be somewhat less than 7000 feet.  Let's hope there aren't any 8200 foot peaks there with trees on top.

You are right, and I missed the QNH, which makes the third option actually correct, although the explanation is missing a rather crucial step then.

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text:
Is there a name for the fast decline + pull to climb pattern?
I'm a hobby photographer and I've noticed some patterns in the bird flights, so I tried to poke a bit into the aviation terminology for it. Phalacrocorax carbo does this movement similar to the attacker's 3 in the Displacement roll when declining just slightly above the water and then it pulls itself up slightly by doing this roll first, then slight pitch movement to continue the declining curve but to also gain some altitude while braking the movement and afterwards switches to gliding above the water.
Sometimes these movements are seen in action movies, so I think there might be an aviation term for it although perhaps only for the full "fighter maneuvers". Any ideas?

Example with the bird's flight trajectory:

Edit: I think the wind is coming under the bird's chest or from the side and I don't think I've ever seen a bird utilizing the same pattern in windless or in very weak wind environment (in those cases it was mainly gliding without turns or climbing).

Welcome Peter, I'm not sure I understand the whole pattern you're describing (because you mix the pattern description and the bird actions to follow this pattern). So far my best guess is you're describing a descending turn close to the water followed by a turn at water level, constant altitude, like in the part 3 you show on the picture. Also is that similar to this (3rd picture)? or that.

@mins thanks. Yes, it's similar to the 3->4 stage of this link. So far the descending turn + turn + constant altitude match the pattern. I guess there isn't a fancy naming for it as for "Displacement roll" or likes, right?

Do you think it is a dynamic soaring technique, i.e. does it appear to be extracting energy from the wind gradient?  I.e. are climbs consistently performed with a headwind component and descents with a tailwind component?  Which direction is the wind from, in your description?  Or does it do the same thing even when there is no wind?  I think birds make brief use of dynamic soaring techniques to extract energy from the wind gradient much more often than is commonly believed, even if it does not result in full-blown long-term-sustained non-flapping flight as per the albatross.

PS any climb that is performed or enhanced by exchanging airspeed for altitude is called a "zoom climb", but that's only one small part of the full pattern you are describing--

@quietflyer exactly the thing! It's even confirmed by Albatrosses utilizing this for long flights and Rayleigh's quote.

@quietflyer feel free to post it as an answer, so I can accept it. (wiki with the description) :)

It would be helpful if you would edit the question to address which way the wind is coming from and whether or not you've seen the maneuver performed in calm conditions also---

@quietflyer edited

There are a couple basic fighter maneuvers called High Yo-Yo and Low Yo-Yo that are kinda similar to what you are describing, but I don't think the bird has the same objective.

Totally didn't get the comparison with jet fighters until reading your reference for Phalacrocorax Carbo, aka great cormorant.  The bottom plane is the fish it's pursuing, which makes the entire manuver worth discussing.
Cormorants hunt by diving on slower, more maneuverable prey, which have the advantage of the denser medium (water) to turn and force the bird to overshoot.
As with the upper jet fighter, the bird can increase its maneuverability by slowing down.  This is done by trading speed for height (kinetic energy for potential energy).  The part you are interested in is the result of the top plane rolling sideways to fall vertically, or "slip".  A cormorant, or an aircraft, does this to start a dive without negatively loading its wings, which are usually much more tolerant of positive loads.
If the cormorant decides not to dive into the water, it will abort by rolling out and increasing its angle of attack to glide away.
One last trick the bird may use is to fly away low over the water to take advantage of "ground effect" (less drag for the same amount of lift) while it continues its search for dinner.
As far as the observation that they do this less on calm days, one might surmise that the ripples on the water surface will make it harder to see what is below, making for more "false positives" on its target acquisition system (eyes-brain).

This + an analogy "not to crash into water" made me think that there has to be some tern for that (because similar or the same thing is often present in the action movies where a plane isn't supposed to crash into an urban area), of which dynamic soaring makes the most sense (for the bird) and also encapsulates the patterns you describe, though probably not the weather.

@PeterBadida rolling out of a slip is so commonly used (for aircraft approaching a runway) I'm not sure it has a special name, but great observation (and photo) anyways.


text:
What are the dimensions of the parking apron?
What are the approximate dimensions of the apron aircraft zones, ramp, aircraft stands such as Airbus A380, Boeing B737, F16.

The Apron Planning and Design Guidebook is used in the US. The goal was to provide a one stop shop for all the relevant information. The FAA maintains a list of standards.
Further, there is special CAD software for the design of airports. This includes the turn radius planning for a large number of aircraft.
Finally, because of the complexity and the large number of regulations there are companies, that specialize in airport planning and design.
Or you could always just wing it like the Germans and be ten years late and six times over budget and still incomplete ...

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text:
Can I get a 20/40 requirement waiver after cataract lens replacement?
I have had lens replacement surgery and now one eye is focused at 16” (close, reading distance)and the other eye is focused at a distance. I have 20/20 vision both at 16” and at distance as long as both eyes are open.
I have a third class private Pilots license and my medical is due. Can I get a waiver because I don’t meet the 20/40 requirement with either eye closed?
For example when my left eye is closed I can not meet the 20/40 requirement with my right eye when it comes to the 16” test and the same goes for my other eye when it comes to the distance test.

Do you need the third class, or can you get BasicMed?

If you are a member of or join AOPA I recommend consulting AOPA member services for help with questions like this. I have consulted them multiple times and they always get a good answer for me or set me in the right direction.
Of course you can consult an Aviation Medical Examiner (AME) first but I recommend you figure out what you need to do and go into your AME knowing you’ll pass the medical exam... once you’ve failed it can be a nightmare to get your medical back and take a long time (and cost lots of money).
Source: I’m a pilot who has used this service of AOPA before


text:
What operations during preflight and pre-takeoff engine run-up cause a change in engine rpm?
In a Cessna 182, during certain preflight check procedures with the engine running, RPM drops. What are these procedures and why does rpm change?

@Jim, Are you now saying you that you are not sure what action or "operation"  you did to cause a drop in RPM?

It was carb heat, I was in the right seat. However I think the answer below is a great answer to the reworded question, and fulfills my curiosity on the subject

You will get a change in engine speed doing a mag check, cycling the carburetor heat, if equipped, and cycling the propeller governor.  You will also see a drop in oil pressure and a rise in manifold pressure when cycling the propeller governor as well.
The reasons?
Carburetor heat increases temperature of the mixture passing through the carburetor, thereby decreasing its density.  Consequently, as the same amount of fuel is being metered into the air steam in the Venturi throat as before, this causes the mixture to become richer and the engine to produce less power and run slower than before.
Mag checks involve turning off individual magnetos, causing the combustion in the cylinders to become less uniform, resulting in a power loss and slower engine speeds.
Cycling the propeller governor causes the governor to slow the engine by increasing the angle of attack of the propeller blades.  This creates a greater workload on the engine.  Lower engine speeds also cause the engine driven oil pump to turn slower, decreasing the oil pressure. And, as manifold pressure measures the pressure of the intake air at the cylinder head, an increase in the workload increases the air pressure at the manifold, causing the spike in indicated manifold pressure with the prop governor set to its lowest speed setting.
Cowl flaps are simply moveable panels which can alter the flow of cooling air around the engine to better maintain engine cooling at low speeds when ram air flow through the cowling is limited.  I’ve never heard of a situation where cowl flap position causes an engine to run slower or faster, though the cylinder head temperatures will change quite a bit and there is a risk of overheating and damaging an engine if you are running at high power settings at low air speeds for extended periods.


text:
How does an operator change an aircraft's maintenance program from high-interval to low-interval?
I have question for CAMO operators. If you have a maintenance program that is high-interval and the aircraft operates in excess of the maximum permissible hours and cycles you must go to a low-interval maintenance program.
How do you do the bridge check from high-interval to low-interval if you find yourself overdue for a low-interval check when you make the switch?

Can you provide a reference to the specific EASA language mandating the switch from high to low?

It is from EMBRAER SMRD:
link

That looks like it mandates a switch from low to high, not from high to low. I'm not as familiar with EASA, but it seems to me that you can always have a more stringent program than the minimum required. I'm sure someone else here will be able to give you a more practical answer.

Yes because I showed the low utilization SMRD not for high utilization. But it doesn't matter! it may also apply the other way from low to high. How do you change intervals to have proper remaining, beacuse the interval may be shorter or longer. Example: you have in high interval that you have 50% remaining, but when you go to low interval you are overdue, because the interval is shorter.

Ah, understand now. I've suggested some clarifying edits based on the comments; please roll back if they don't capture your meaning.


text:
Is there any common research model for supersonic transport?
Is there any common research platform, like the Common Research Model of NASA for supersonic transport flight?
I assume that in aerospace industry, every company has his own research platforms depending on previous projects but was there any common model that companies shared for this purpose?

Does any major company even research supersonic transports?

Of-course they do, if it's not always internal they just outsource it to research centers (NASA, ONERA, DLR etc.), or universities. http://www.cbc.ca/news/technology/airbus-patents-supersonic-plane-that-could-hit-mach-4-5-1.3178955

What about this: https://lbpw.larc.nasa.gov/sbpw2/propagation/lm1021/?

@MarkJonesJr. Great! That's indeed an answer to the question, the CRM was also studied for the other workshops (high-lift etc.) so we could consider this one a common research supersonic platform at the moment.

@MarkJonesJr. You could update your answer, for me to accept it.

@AlexandrosK. done.

According to NASA here:

This test case is an aircraft concept previously used as an optional
  case (LM1021) in the 1st Sonic Boom Prediction Workshop. This
  configuration is described in the following reference: John
  Morgenstern, Nicole Norstrud, Jack Sokhey, Steve Martins, and Juan J.
  Alonso, “Advanced Concept Studies for Supersonic Commercial Transports
  Entering Service in the 2018 to 2020 Period,” NASA
  CR-2013-217820,DOI:2060/20130010174. See NTRS Record. There is also a
  description in the following reference: John M. Morgenstern, Michael
  Buonanno, and Frank Marconi, “Full Configuration Low Boom Model and
  Grids for 2014 Sonic Boom Prediction Workshop,” AIAA-2013-647.

Interesting but I am asking for a common research model, i.e. a model that was shared between other aerospace research centers throughout the world, like ONERA, DLR etc.

@AlexandrosK. I thought as much but couldn't find something equivalent.


text:
How do foreigners (international students) work as airline pilots in the USA?
I am planning to study in the USA/Canada (whichever is easier to work afterwards) to get my pilot licenses from 0 to CFII or CFI-MEI, so my best bet is to apply for an F-1 visa program (since it grants 1 year working permit upon completion of my study).
So my question is how can I apply for an airline first officer position after getting 1500 flying hours? What else do I need? (I assume its working permit aside from the one granted by F-1 visa since it's only valid for on-campus jobs and it would be already consumed in getting my 1500 flying hours).
Any correction for the info stated would be much appreciated.

By the time you have 1500 hours you will probably be at the end of the 1 year working permit period of the F-1 Visa. Will you be applying for an H-1B1 Visa? Or is that your question? Also, I think the F-1 work permit is for work related to your educational curriculum.

i believe there is an annual flight hours limit of 1000 h for pilot, and a monthly limit of 100, thats not the case, the case now is what are the chances of getting H-1B1 visa, because there is absolutly no chance of getting hired at my home country. and for the F-1 visa its valid for 1 year upon completion of the study and only for on campus jobs and its non-renewable


text:
Why do airlines in the United States of America use total time as an eligibility requirement for employment?
Airlines in the United States of America have varying total time requirements to determine eligibility for the potential employment of applicants. Why do airlines set total time requirements beyond the minimums that are present to achieve the required ratings?
I realize that this question is prone to answers that are purely speculative or opinion based, so I caution against posting such an answer. I am asking for concrete reasons. For example, airline executives may have given answers in the form of interviews. I also speculate that airlines may have insurance requirements or institute total time requirements to control the number of applications they get.

For what it's worth, back in the early 1980s when I was trying to get on with an airline, it was commonly accepted that what you said in the last part of your last sentence was the reason, i.e. to control the number of applications they get. Of course, many of us sent our less-than-minimum-time applications anyway because we desperately wanted to fly for an airline. However, I never knew of any low-timer that was hired unless they knew somebody. United did interview low-timers once for possible strike breaking.

Back in the late 90's American Eagle was hiring commercial pilots with as little as 500 hours total time and no ATP, obviously. Tough way to build time (low pay, you have to accept any base they send you to, etc.) but unless they sent you to the Caribbean it was all jet time. They called them "500-hour wonders." :)
The reason I point this out is that not all airlines can afford to have high TT requirements, not in a market where there is a scarcity of candidates.

"Why do airlines set total time requirements beyond the minimums that are present to achieve the required ratings?" Because you learn a LOT more about piloting in the 1000+ hours after your rating than you did while prepping for the rating. Though I would say that a junior pilot with a few hundred hours can still be a very capable First Officer if the Captain is a multi-thousand hour pilot who really knows the aircraft.


text:
Why aren't the CVR and FDR required to store data for a longer period?
I'll be honest I don't know a lot about the brand new airplanes, but one think I do recall a lot of from reading accident reports is that they typically only recorded the last 30 minutes of data.
When an aircraft costs over 30 million USD, with some costing in excess or $300 million, surely being able to increase the amount of data recorded 10x or 20x pales in comparison to the costs?

Possible duplicate

Downvoted due to factual inaccuracies in the question: CVR's store each channel for 30 minutes, but the area mic (or, the sum of everything being said & heard) for 120 minutes.  Modern FDR's store far, far more than 30 minutes of data.

@RalphJ A lot of questions here come from a misunderstanding of the facts. 30 minutes is a common misconception too so in my opinion it doesn't deserve a downvote.

CVRs typically store two hours of voice recordings (source).
It simply wouldn't serve any purpose to store longer recordings.
It is extremely rare for an emergency to last for such an extended time.
Qantas 32 was one of the longest emergencies in recent memory, and it was only 1:45.
The MH370 flight was longer, of course, but it still hasn't been recovered.
While I'm sure it is technologically possible to record more voice data, that would primarily record innocuous and routine conversations among the pilots.
I suspect that the pilots, and their unions, are reluctant to have their mundane and irrelevant conversations recorded and inspected.

Good points, I was just thinking about the recent incident of the near-miss at SFO, supposedly the CVR wasn't turned off and the entire incident was wiped from the recorder, something that would have been avoided if it had the ability to record longer. Also I would imagine that data would be protected under existing data privacy laws and would only be accessible in the event of an incident, with regards to your point about pilot convesation privacy.

"would only be accessible in the event of an incident" is very important, especially in the context of AC759.  There was not actually a crash, and the plane landed safely.  While everyone would love to know what the pilots were thinking/saying, CVRs cannot be pulled arbitrarily.  The NTSB has rules about how pilot recordings can used / must not be used.

I don't think anyone would be surprised if you called the event an 'incident'. The plane was only a few feet from landing on top of two fully fueled airliners waiting on the taxiway. And like I said, the data would remain protected, as I assume it is now, and can only be pulled when a serious incident occurs, like the near miss at SFO. Im sure the NTSB and other regulatory agencies have already set the benchmark for what classifies as an "incident" and whether to pull the recorders data.


text:
How does the aspect ratio of a wing impact its lift?
The wing lift formula shows that lift of a wing is proportional to its area.
$
L = {\dfrac 1 2 \times \rho V^2 \color{magenta}S C_L}
{\small
\begin{align}
&{} &&\text{where:} &&L = \text{lift,} &&\rho = \text{density of air,} \\
&{} &&{} &&V = \text{velocity,} &&\color{magenta}S = \text{wing area,}\\
&{} &&{} &&{}&&C_L = \text{coefficient of lift.}
\end{align}}
$
So why are most conventional wings shaped the same (swept back rectangles)?
Imagine a conventional airplane but with the wings shaped as 2 thin long rectangles attached to a fuselage from the cockpit until the tail with the same area as the original wing.
With all other things (like angle of attack, etc) being equal will the same lift be generated as the original wing?

@mins your comment may be a good answer

To summarize my understanding - the formula is accurate. The lift WOULD be the same in both scenarios  However the thinner longer wing create significantly more drag. This would require more thrust from an engine, thereby making it less efficient but still (theoretically) capable of flying?

@skanga, the formula is accurate by definition. It does not imply that lift is linearly proportional to wing area, because the $C_L$ is for specific wing, not universal. It is roughly proportional to it, but not exactly.

doesn't sweeping a wing give more wing area with less total width of airplane?

@skanga, "the thinner longer wing create significantly more drag". Could you please elaborate this statement? I am not sure your statement is true or not, but as far as I know, the longer the wing required less power to make it fly. Glider i.e, has aspect ratio around 20 to 30.

@JanHudec, "The formula does not imply that lift is linearly proportional to wing area, because the CL is for specific wing, not universal". Very interesting. So, how to bind the lifting formula to the wing area and the aspect ratio?

@AirCraftLover, the common formula above is a useful approximation, but you have to be aware that the coefficient of lift (and the critical angle of attack) changes with chord length.

@JanHudec, when an airplane is take off, it extend the slat (in leading edge) and the flap (trailing edge). That is intended to extend the wing area, which will give more lift following the equation above. I agree with you that drag and lift are two inseparable things. But as long the AoA is within the allowable range, the lift is much grater than drag.

@AirCraftLover, except simple flaps (used on smaller aircraft) don't extend the area, only increase camber, and so do the control surfaces—and they still change lift.

"The wing lift formula shows that lift of a wing is proportional to its area".
That's absolutely true. However a wing generates both lift and drag. Drag is of two natures: Parasitic drag and lift-induced drag. The sum of all drag is the total drag:

Source: Wikipedia
Induced drag decreases with speed, and has its origin in wing tip vortices. Vortices actually increase the velocity of the downwash, and changes the effective angle of attack. Which in turn changes the direction of the aerodynamic force, creating a force opposing to the direction of flight:

Induced drag, source: Wikipedia
Induced drag being due to tip vortices, if we can make vortices less efficient, then we also reduce induced drag. The way to do that is to have long wings, so the the downwash from the vortices affects only a part of the wing:

Tip vortices, source: Wikipedia
Research demonstrated that the induced drag is dependent on the wing aspect ratio, not only on the wing span. This can be understood easily: The quantity of air in a tip vortex is larger when the chord is large.
So the answer to your question is: Yes lift is proportional to the wing area, but the lift/drag ratio is proportional to the wing aspect ratio. That's why longer wings are preferred, they minimize energy lost in fighting drag.

"Why are most conventional wings shaped the same (swept back rectangles)?"
Longer wings are better for fuel efficiency, but we have other problems in the designer queue, and some can be solved by selecting the wing planform, e.g.:

We want to prevent the stall to be abrupt (at the expense of creating less lift though):

We want to delay the creation of a local supersonic flow in supercritical wings used in commercial airliners. When flying at M 0.8, airflow is accelerated to produce lift, some areas of the wing reach supersonic speed (Mach > 1). The associated shock wave creates an additional drag. By sweeping the wing we add a spanwise component to the airflow which decreases the chordwise velocity, so the shock wave appears only to a higher aircraft airspeed:

On the other hand, the sweptback wing tends to stall at the tip first, which is not good at all, as when a stall appears we need ailerons to prevent it from worsening, and ailerons are located at the tips to increase their effectiveness. So swept wings are also twisted so that the tip angle of attack is smaller than the root one, forcing the stall to start at wing root.

Wings planforms are multiple, each type of wing, or sometimes subcomponent, can improve a particular issue (possibly creating another that will be less important for the designer). See this very interesting article on Wikipedia: Wing configuration

I quoted this: The quantity of air in a tip vortex is larger when the chord is large. This is answered my long question in my mind, and it is make sense. Thank you my friend for the nice explanation.

Quote: On the other hand, the sweptback wing tends to stall at the tip first. What is that mean? How comes?

@AirCraftLover: The sweep-induced spanwise flow creates a low energy boundary layer at the tips. When the wing nears the critical angle, the flow separates first at this place (unless the effective angle of attack is lowered by some geometric or aerodynamic twist). See this detailed explanation.

A higher aspect ratio (given the same wing area) means more wing span and less lift-dependent drag. At the same angle of attack, higher aspect ratio also means more lift (within limits).
Lift is produced by deflecting the oncoming stream of air downwards. The more air can be affected, the more efficient lift production becomes. Maybe you want to read a few answers around here if you want to learn more.
What you describe is a slender body wing. Most of the deflecting is done by the first few percent of this wing's chord, and the remainder will not be able to increase lift more, working on the already deflected air. Consequently, the same area of wing will create less lift force, at least in subsonic flow. Take the XB-70, for example: Its maximum wing loading (mass divided by area) was 420 kg/m². The swing-wing B-1, which could stretch its wings out for slow speed flight, has a maximum wing loading of 1190 kg/m², however, the calculation method of its wing area does not include the large delta section ahead of the main wing. Still, a sizeable difference remains and shows that the same wing area can create more lift when stretched out.

your words: "Most of the deflecting is done by the first few percent of this wing's chord, and the remainder will not be able to increase lift more, working on the already deflected air.". YOU MEAN ONLY 25% OF WING'S CHORD DEFLECTS AIR?

@DavidTeahay: No, not at all. The forward 25% of the wing contribute as much  deflection as the rear 75%. The ratio is even more skewed in a slender body, where half of the deflection happens right at the nose. Now you might think that you only need to cut those 75% off and still have half the lift, but no, that rear part enables the forward part to contribute so much more. Cut some of it off and you will lose lift in proportion to that.

Okay...understood, thank you!

The "wing lift formula" that you quoted is a simple approximation and is not
used for the detailed design of wings.
Practical reasons why conventional wings have the shape they do depend on
many design considerations, including the mission of the aircraft. The
answers you have received address some of those issues.
Be aware though, that there are many misconceptions in wing design.
One common misconception is that:
"Induced drag being due to tip vortices, if we can make vortices less efficient, then we also reduce induced drag."
That is a great over-simplification. Induced drag depends on the shape of the entire wing, not just the aspect ratio and the tip vortices.
Former Boeing Technical Fellow Doug Maclean discusses this misconception in
particular, and many others in his book:
Understanding Aerodynamics - Arguing from the Real Physics.
You might get a lot out Maclean's talk:
Common Misconceptions in Aerodynamics

Great book by McLean.


text:
Do (did) powered airplanes exist where pilots are not in a seated position?
Well... all is said in the title. I mean "traditional" powered airplane, with a cockpit and long flight capable, not a paraglider.
Upright pilot or prone pilot would qualify.
Likely experimental or military.

Source
The concept was once studied with the XF-90, but didn't get to reality.

If you count hang gliders and weight-shift as aircraft, then there are quite a few :)

If you mean airplanes versus aircraft you might want to edit. Also, do you mean still flying or any historic airplane/craft?

A bit related.

Also see this: https://en.wikipedia.org/wiki/List_of_prone-pilot_aircraft

And of course, the most famous aircraft of all

@RonBeyer Not strictly an aircraft, but a powered flying machine.  I see your Wright Flyer and raise you the Lunar Excursion Module

@Simon I think you win, the LEM is probably the longest distance manned flying machine ever created :)

@mins With tongue in cheek, there are several types of flying machine that do not require aerodynamic lift.  Consider the Giffard dirigible for example.

Most modern airliners could be fitted with a couch or beanbags for pilot comfort in flight, but it looks much more professional to sit up looking forwards at the clouds.

@Rich What happen on turbulence then?

@Martheen Obviously, the pilots would merely have to buckle down in their beanbags before they encounter turbulence.

Would jetman fit the bill?

In the first ones the pilot was rarely sitting. Inspired by ships, some early aviators steered their craft by standing upright:

Almost all balloons were and still are flown standing upright. Same goes for all Zeppelins, and they should qualify as powered aircraft.
All Lilienthal glider designs required the pilot to stick the forearm through a tube and grab a horizontal bar, so his weight would rest on the forearm. Steering was done by swinging the legs left or right rsp. back or forward. The legs also doubled as the landing gear, much like in modern hang gliders. Lilienthal experimented with carbon dioxide engines, so some of his gliders can be called powered.
Gustave Whitehead's Number 21 design of 1901 was flown standing upright, but it is disputed that he actually flew it successfully.
The early Wright Flyers were flown in a prone position. Sitting came later.
The Santos-Dumont 14bis of 1906 was flown standing upright. Similarly to the Wrights, Santos-Dumont's later designs like the Demoisielle had a proper seat.

Santos-Dumont training to fly his 14bis (picture source)

The Horten gliders were flown in a prone position so the pilot would present a lower cross section. The Horten IIId was a motor glider version using a 32hp Volkswagen engine, so this should count as powered, too.
Before anti-g suits were perfected, some designs used a prone pilot position to increase the possible g loads. Here is an answer which covers this aspect.
René Leduc's ramjet-powered experimental aircraft used an almost lying position for the pilot to keep the cross section of the centerbody small.

Yvan Littolff in the cockpit of the Leduc 021 (picture source)

Most hang gliders use a prone or almost lying position for reducing the drag the pilot causes. The powered ones should also qualify here. Same goes for motor gliders derived from sailplanes, where the pilot position is almost lying, too.

Yes, but probably not what you have in mind.
The Hiller Pawnee had the pilot in a standing position.
Some weight-shift hang glider pilots are prone.
Hot air balloon pilots stand up.

I would also submit the Henschel Hs-132
Never flew, but four were built.
Based on the Volksjager
WW2 had the most gorgeous aircraft.....now everything is all angles and who can lock on and fire their missiles first.....

The Hs-132 was an independent design and quite different from the He-162. Only the configuration was the same.


text:
What is the purpose of wide area multilateration?
From what I understand the wide area multilateration (WAM) technique is similar to Loran-C but reversed:

The aircraft ADS-B transponder broadcasts a signal received by several ground stations.
The differences in time of reception draw hyperboloids of revolution in space, their intersection is the aircraft position.

Multilateration principle

What are the intended uses of this inexpensive system which seems redundant with ABS-B, GNSS and SSR? Are aircraft in the world already using WAM? Is multilateration intended to replace other system(s)?

3 receivers is not sufficient. You need at least 4. If you have receivers A, B and C, You can create 3 hyperboloids: P(tA-tB), P(tA-tC) and P(tB-tC). However, the information in the third parabola is exactly the same as in the difference between the first two, so it doesn't bring you anything mathematically. To solve the problem, you need 4 measurements. This allows you to create a set of 4 linearly independent equations which allows you to solve the problem of the 4 unknowns (X,Y,Z, transmission time). The transmission time you don't explicitly need but you can't do without.

Wide Area Multilateration (WAM) is used as an ATC surveillance system. Like Secondary Surveillance Radar (SSR) it is classified as a cooperative independent surveillance system; the aircraft has to cooperate (i.e. an active transponder) but position is determined independent from data sent from the aircraft (unlike e.g. ADS-B).
A WAM system relies on Time Difference of Arrival (TDoA) measurements to determine the position of aircraft. At least 4 receivers with synchronised timing are needed to calculate the position of a transmitted signal. In practice WAM systems have a redundancy built in to them and are operated with more than 4 receivers. It can operate purely passively but usually the system will interrogate aircraft transponders to ensure a sufficient update rate can be maintained. This is a downside of the system; with its omnidirectional interrogators it is often considered as using much capacity on 1030 MHz, causing an increased transponder load (every incoming interrogation needs to be processed by a transponder, even if it is intended for another aircraft and no reply is to be given).
The system is used as an alternative to secondary radar. The installation of a receiver is much cheaper than a radar, but the life cycle cost of the surveillance system depends also on site renting costs, communication costs and maintenance cost. Maintenance tends to be cheaper (no rotating radar head), but communication is more expensive (more lines). Overall, WAM is a cost effective alternative to SSR.
WAM is able to achieve very high accuracy and high update rates when a sufficient number of sensors are installed. For example, German Air Traffic control DFS operates the Precise Approach Monitoring system in the Frankfurt TMA with 36 receivers and achieves and accuracy better than 25 meters with an update rate of 1 second.
In mountainous terrain, valleys can be covered by installing receivers on mountain peaks, which is much cheaper than covering it all by radars. Austrian Air Traffic Control AUSTROCONTROL operates a nationwide system consisting of 60 receivers.
In terrain that is difficult to access for maintenance or where there is no infrastructure to install radars WAM may also provide a solution. On the North Sea both Dutch (LVNL) and British (NATS) Air Traffic Control operate WAM systems to provide air taffic surveillance services to helicopters operating on the oil platforms. Receivers are installed on oil platforms.
WAM is used around the world, other deployments include for example Afganistan, Australia, Denmark, Ghana, Namibia, USA and many more.
The system can at the same time provide an ADS-B data stream from received ADS-B messages and can add extra security checks by comparing measurements of the data sources.

It can be independent of GNSS (at least for outages up to a day or two) and isn't relying on the airborne equipment correctly reporting position, as pure ADS-B does.  It's also potentially a lot cheaper than SSR.


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From what distance can a man hear and see an airplane flying overhead, without any equipments?
Suppose I stand at p = (latitude,longitude) on earth. I want to manually check for any airplane flying overhead in my neighborhood with naked eye and without any equipment.
I scan air-traffic radars for every plane in the vicinity of my location meaning probe_region: latitude ± δ , longitude ± δ (we assume a region of square geometry for simplicity)
1- How far away can a man hear the jet engine of airplanes? Meaning what should be the radius of probe (or in this square case ~δ)
2- How far away can a man see the body of an air plane in clear sky with naked eye?
I'm looking for answers in kilometers or miles. (converting from radius in kilometers to (lat/lon) interest_box is another problem, like 1 deg in latitude is ~110 km)
In the diagram below, the plane inside the blue bound can be heard from p but the plane just outside of it can't be heard (I assume we can hear engines sooner than we can observe the whole plane)

Maybe specify the engine type and number of engines?  Planes are getting quieter.  For a loud one, see https://aviation.stackexchange.com/questions/21683/did-the-xf-84h-thunderscreech-really-cause-900-sonic-booms-per-minute.

@AnonymousPhysicist I just want approximate bounds. Assume largest plane and loudest engines in the commercial market.

Maybe a 727 during takeoff?

I regularly hear aircraft passing overhead at FL360 or higher (approx. 6 nautical miles high), if I'm away from other sources of noise. I definitely don't hear them very far laterally laterally though. Aircraft can be seen with the unaided eye at that altitude but it's very difficult to find them in the first place unless they're creating contrails that lead to their position.

Do you need to be able to identify the shape of the object as a plane? Or is a pinprick of sunlight glinting off a fuselage sufficient? Stars, for example, are visible at distances of trillions of kilometers, although they have effectively zero angular diameter so their shape cannot be resolved. But we can still look at the sky and easily identify that something is there. Similarly, a plane could theoretically be visible at distances much farther than the distance at which you'd be able to visually identify it as a plane.

Whose ears and eyes are we using? Sadly, my ears don't quite hear as well as they used to (invincible teenager listening to loud music against parent's recommendation), and my eyes don't see as well as I'd like them to (despite new contacts). However, a good friend of mine can read small text at distances where I can't even make out that there is text to be read.

The box should be a circle... an aircraft just outside the box at the midpoint of a side would be closer to the observer than an aircraft just inside the box at a corner.  But beyond that...

... there is so much "it depends" involved here that any answer is only good to about an order of magnitude.  Something with older, loud engines at climb power will be detectable much farther than something new like a B-787 at cruise power. Then there's aircraft altitude. And ambient noise for the observer. And atmospheric conditions. And aircraft size and aspect. And ambient light. And cues like contrails, sunlight glinting off metal surfaces, and so on. Any number you get that applies to "this" case may be far off for many other cases.

I seriously doubt you would always hear the plane before you see it. Also you haven’t factored altitude which can change things a lot. And of course weather and the time of day as well.

It depends on the altitude and orientation of the aircraft as some aircraft will have a larger cross sectional area depending on which way its facing and where you are standing. Depending on the altitude of the aircraft its eventually going to disappear over the horizon. The angular resolution of the human eye is somewhere in the area of 0.03 degrees so ultimately you will be able to see an aircraft when its relative size to your reference is in excess of 0.03 degrees (weather or not you can tell its an aircraft is likely up for debate but you should be able to physically resolve it). You can use this calculator to check it out but for reference a 737 is about 12.5m tall so with a 0.03 degree minimum resolution you should have the ability to resolve it up to 24km away however in my practical experience that very much depends on your relative position to the plane, the clarity of the air, and the time of day/night. 24Km is ~13Nm (how pilots think about distance) which you might very well be able to see on a clear day.
Sound intensity will decrease exponentially over distance but your ability to hear something will depend on other ambient noise in your local area, your hearing ability, the frequency of the engine noise (and there is dopper shift in play here) and reflective surfaces en-route. If you take a look here some sonic booms (not necessarily engine noise) can be heard as far as ~80NM from the source. Here is a fun calculator to show you the effects of sound dampening over distance (unfortunately it only works out to 1000 meters)

A reasonable approach, but the limit of resolution being 0.03 degrees does not mean that things smaller than 0.03 degrees are invisible. It means that you can't distinguish between objects closer than 0.03 degrees. You certainly couldn't tell the shape of a plane at that distance, as you couldn't even distinguish one wing from another, but you still might be able to see a featureless dot in the sky at a longer distance.

Just now, there is a Lear 35A going directly over my house at Fl36.
I could see the contrail, and just barely see the jet shape at the head of it.
But only because I knew exactly where to look, and the contrail. If it were not for that long contrail, there is no real way I would have found it before it went out of sight.
I heard nothing.


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How does WAAS improve the accuracy of the GPS?

The satellite constellation in the United States is called WAAS, which stands for Wide Area Augmentation System. It consists of 38 satellites, three ground master stations, and three geostationary satellites. Though the US GPS constellations works globally, other regions have developed similar constellations. The European equivalent, completed in 2016, is aptly named Galileo.
Source

How does WAAS improve the accuracy of the GPS?

Have you tried researching existing sources of information?  There's plenty out there... https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/laas/howitworks

That quote is simply wrong. The US GNSS is called GPS, and the European one is called Galileo. WAAS is an add-on to GPS to get better performance. See https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System for details

@AircraftEnthusiast007 WAAS was developed and is operated by the FAA. It is clearly aimed at usage in aviation, so this question is perfectly on topic here. It might also be used by other receivers today, but aviation is definitely the main purpose.

https://aviation.stackexchange.com/questions/11426/how-accurate-is-inertial-positioning

The fact the quote from someone else contains incorrect statements is not a reason to downvote the valid OP question.

In short
WAAS, wide-area augmentation system evaluates errors on GPS satellite signals, and broadcast applicable corrections to GPS receivers located in North and Central Americas. Errors detected include satellite clock errors, ephemeris (orbital elements) errors and atmospheric delays. The corrections are sent using satellites orbiting higher than GPS satellites, 36,000km vs. 20,200km, but using the same L1 carrier frequency (1.5GHz) as GPS, and the same modulation techniques.
A receiver listening on L1 receives both the GPS ranging messages and the WAAS correction messages. It applies corrections when calculating its position. Correcting ("augmenting") GPS with WAAS increases the GPS typical 30m-precision (95% limits) to about 3m in single-frequency receivers.
Delay is the most critical parameter. Waves are slowed down and refracted in the atmosphere layers (adding up to about 60m to the path of L1 wave). This makes satellites appear at distances larger than they are, and leads to erroneous calculations.
Corrections to be applied are determined on the ground using a network of 38 GPS reference stations (WRS) distributed over North and Central Americas. Corrections are uploaded to general-purpose geostationary satellites hosting a WAAS transmitter and, like GPS signals, corrections are blindly broadcast to whoever listens. The satellites cover all Americas, however WAAS signals are only beamed to the Northern hemisphere as there are no WAAS reference stations to evaluate the corrections in Latin America (ICAO currently evaluates SACCSA hosted on Immarsat for CAR/SAM regions).
WAAS is operational since 2003, it is one of the existing augmentation systems, designed to improve GPS (and other GNSS) use. Like GPS was the first GNSS, WAAS was the first implementation of ICAO SBAS, satellite-based augmentation system. This is how GNSS and SBAS cooperate:

(Source)
WAAS was intended to provide aviation with a signal-integrity guarantee (main goal) and an approach-class positioning. The WAAS signal received and demodulated by the GPS IC, most GPS IC are now WAAS-capable (e.g. popular SiRFstar sensors support WAAS since 2004), so WAAS use is nearly generalized today, from smartphones to hi-precision surveying stations.
For a receiver not located in North/Central Americas, another SBAS must be used, e.g. EGNOS provides corrections in Europe, for Galileo and GPS GNSS.
Do not confuse SBAS (WAAS, EGNOS, etc), the augmentation system, and GNSS (GPS, Galileo, etc), the positioning system. A SBAS cannot be used alone, it only evaluates and broadcast errors for one or more GNSS signals. Of course a satellite carrying a SBAS transmitter (SBAS messages) is not prevented to also transmit a GNSS signal (navigation message) on the same and/or a different frequency, and some do, but that's two different things.
Plenty of details follow.

Refresh on GNSS principle
A GNSS satellite is basically an atomic clock delivering a time service by radio. It emits 6-second-long data streams (subframes), data including the time the first bit of the next subframe will be precisely sent, allowing a receiver to measure the transit time of the next subframe. When merged, the subframes form a repeated 750-second digital navigation message containing, in addition of the time information, essentially fixed or slowly-changing data, like an identification and orbital elements (orbit eccentricity, inclination, etc). A GNSS receiver use the time-stamps and other data from the navigation message to determine:

The satellite position when the current subframe was sent using the orbital parameters and the departure time known from the previous subframe.

The distance between the satellite and the receiver from the time of departure and the time of arrival.

Its own position from the the satellites positions and distances.
This requires to determine X, Y, Z coordinates in WGS-84 coordinate reference system and the unknown bias between the receiver and the satellites clocks. To solve the four unknowns the receiver must have four satellites in sight. It determines four satellite positions and pseudo-ranges (a pseudo-range is a range computed using the biased receiver clock for the arrival time) to create a system of four linear equations.

In this process, any error on a satellite orbital element, on a satellite clock or in the assumed wave path translates in an error on the position calculated by the receiver.
Refraction and atmospheric delay
Errors mentioned above are labeled (1) and (3) in this error recap:

(Source)
Propagation delays (3) are observed because:

$c$ velocity is less in air than in vacuum, and varies with air composition and altitude. This introduces a ranging error of about 30m.

The wave crosses different layers of air with different and opposed gradients of refraction index. This slightly bends the path, in one direction, then the opposite. At L1 frequency (1.5GHz), the distance traveled can be increased by 30m. The delay vary with the elevation angle, hence with the receiver location.

Atmospheric effects vary with frequency, dual-frequency receivers like military and land surveyors ones are able to infer the current delays and can correct a satellite range themselves but single-frequency receivers cannot, this is where WAAS comes on.
WAAS and SBAS
WAAS is the SBAS for North/Central Americas providing corrections and alerts regarding the GPS, the US GNSS. It consists in a network of 38 GPS ground stations in North and Central Americas (Wide-area Reference Stations) receiving the GPS L1 signal and determining for each satellite in sight:

The satellite clock error.
The orbital elements errors.
The delay introduced on L1 by atmosphere.
The satellite signal reliability (integrity).

Europe is covered by EGNOS, Japan by MSAS, India by GAGAN, China by BDSBAS, etc.

(Source)
These systems implement the same ICAO SBAS standard, described in RTCA MOPS DO-229-C minimum operational performance standards for global positioning system/wide area augmentation system airborne equipment:

Summarized in WAAS MOPS: Practical examples.
Exhaustive description in The EGNOS SBAS Message format explained.

All SBAS stations have their actual coordinates precisely surveyed in ITRF using multiple methods. Each station also

Runs an atomic clock to have a precis UTC reference.
Computes its own GNSS position solely based on the GNSS signals.
Perform precise GNSS satellites ranging and can determine the satellites actual orbital parameters by continuous observations.

Corrections for atmospheric delays, which vary between the different SBAS stations, are transmitted as a 5x5° grid of interpolated values. Each receiver selects the square the closest to its position.
A new version of the standard, dual-frequency, multi-constellation SBAS (DFMC SBAS) will be applicable to new SBAS started next year, in order to create a seamless global coverage of complementary SBAS, more precise than the current version, for lower decision heights.
SBAS transmitters can also transmit a navigation message similar to a GNSS navigation message. This navigation message can be used for positioning. This service is not used in aviation with the current version of SBAS, but with DFMC it will be included.
Other ICAO augmentation systems: GBAS and LAAS/GLS
An equivalent, but more precise system, known as GBAS, ground based augmentation system, uses a network of ground stations distributed on a smaller area to compute more precise corrections.
Corrections are broadcast in VHF by ground transmitters instead of satellite-hosted transmitters. To get the corrections, the GNSS receiver must use a VHF reception module in addition of the GNSS IC. GBAS-capable receivers are more complex, more expensive and have more reception constraints.
LAAS, local-area augmentation system, also known as GLS, GBAS landing system, is a GBAS with reference stations in the vicinity of the airport, it is used for landing.
DGNSS and RTK
SBAS (including WAAS), GBAS and LAAS/GLS are actually differential GNSS using range/code measurement to determine corrections, their very fine details are found in differential GNSS descriptions.
There is an alternate way of using GNSS signals ignoring the navigation message data and ranges. It uses the phase of the carrier used to send the message. It is much more precise, but for a single-frequency receiver, it requires a delicate initialization phase followed by a permanent reception of the carrier, two impractical constraints in aircraft.
RTK, real time kinematic is an example of positioning by phase measurement.
Phase measurements, common for precise applications, are usually done this way:

One or more GNSS receivers on the field (called rovers) record phase values at different locations.

At the same time, a reference station, which position is known, usually located at the office, performs identical phase measurements.

When a rover returns to the office (or when its data are downloaded), rover and reference measurement are mixed to determine the locations surveyed by the rover.

In contrast RTK uses a link from the reference station to the rovers, allowing on-the-flight (OTF) positioning, removing the post-processing step. This is what real time means in RTK
RTK increases the precision to the centimeter. It is widely used by surveyors, but also in agricultural and autonomous vehicle applications. However the base station signal is usually a paid service, though some free NTRIP "casters" are available on the model of private ADS-B receivers used on flight-tracking sites.
In RTK static applications, long measurement periods are possible. Millimeter precision is reached by averaging the measures. Such precision allows to use RTK sensors, e.g. to track deformations on structures like bridges.

I would add: GPS is very precise on relative positions (on short periods (minutes), distances< 50km)), just the absolute precision is less precise (usual number you see about GPS precision) ... ... so you just calculate the correction for an airport (and now) so you get much better precision. -- Note: GPS ground stations measure real GPS orbit and send directly to satellites orbital and time correction, but this is part to GPS). -- Note: dual band may be able to compensate a lot of atmospheric corrections (but not as good as GBAS)

Basically, the GPS knows were the ground station is so it knows the height, position etc. So you have a way to verify the calculation of the satellites.
The calculation passes, then, through the WAAS master station and removes any errors. With this, is possible to maintain the integrity and accuracy of the GPS data recevied by the aircraft.

Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

"The GPS {receiver?} knows where the ground station is..."  while that may be true, I'm not sure that this is central to how WAAS works. Can you support your answer with a published source?

@RalphJ: I agree. What makes GNSS Augmentation work is that the ground station knows where itself is.


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Elevator or Aileron?
I was just looking at an airplane take off, and when it was taking off, some flaps were facing down at the back of the main wings-
Are these Ailerons or elevators please? I did some research but the internet said that the tail flaps are elevators only?
What am I missing and why did the pilot bring those flaps down when taking off?

Hi I added an image

One arrow points to an inboard flap, the other to an aileron.  Which arrow are you asking about?

Hi both actually, I thought that it would be better to just have one long flap, and use that just for take off, and so take off would be much easier?

Wikipedia has a useful page on flight control surfaces, which includes this image:

(Credit: Wikimedia Commons)
The item labeled inboard flap may be the items you are asking about.  From that page:

Flaps are mounted on the trailing edge on the inboard section of each
wing (near the wing roots). They are deflected down to increase the
effective curvature of the wing. Flaps raise the maximum lift
coefficient of the aircraft and therefore reduce its stalling speed.
They are used during low speed, high angle of attack flight including
take-off and descent for landing.

+1 for illustrating with the mighty 727!

Hi, thanks for the link and explanation! Why doesn’t that wing flag go the whole way along the back of the wing please? Wouldn’t that help more?

@JonathanChing  The trailing edge of the wing also needs room for the aileron which rolls or banks the aircraft resulting in a turn.  The ailerons move in opposite directions, if the left is deflected downward then the left is deflected upward (and vice versa) which your image shows  https://en.wikipedia.org/wiki/Aileron

Is there a reason why the take off flap is longer than the the flap used for turning (aileron) please?

The force required for roll is smaller than the force required for lift, therefore the ailerons don't need to be as big as the flaps.
By the way, ailerons are not referred to as flaps. See https://en.wikipedia.org/wiki/Flap_(aeronautics) and https://en.wikipedia.org/wiki/Aileron . However, sometimes (rarely) they are combined into one device: https://en.wikipedia.org/wiki/Flaperon